How do I optimize my large grass system to render quicker?
I think the best way would be to have very low poly grasses with very low Res textures. But it's not very evident. In my knowledge, at the moment, there is not the equivalent of adaptive subdivision for the hair particle.
On the other hand, I noticed that former versions of Grasswald used less graphic-card memory, than newer, in rendering but it uses still more memory than low poly particles you can model yourself. To go further, the last Grasswald version has an adaptive weight painting depending on the camera's fieldview. But it doesn't works with videos because, when you change the weight painting, the particle system will randomly change each time you change this weight-painting. That's to say if your camera make a travelling, the particle system would randomly change on each frame.
I will make my video but only with grass micro-displacement texture (with adaptive subdivision) instead of any particle system.